1. The Surgeon General's Vision for a Health and Fit Nation 2010;U.S. Department of Health and Human Services,2010
2. US Census Bureau. The older population in the United States: 2010-2050 population estimates and projections. Available at: https://www.census.gov/prod/2010pubs/p25-1138.pdf. Accessed June 18, 2015.
3. Department of Health and Human Services, Administration on Aging. A profile of older Americans. Available at: http://www.aoa.gov/Aging_Statistics/Profile/2013/docs/2013_Profile.pdf. Accessed June 18, 2015.
4. A prospective study of walking as compared with vigorous exercise in the prevention of coronary heart disease in women;Manson;N Engl J Med,1999
5. The Henry J. Kaiser Family Foundation. Healthcare spending in the United States. Available at: http://kff.org/health-costs/issue-brief/snapshots-health-care-spending-in-the-united-states-selected-oecd-countries. Accessed June 25, 2014.